Method of making electrical resistance units and the like



Patented Dec. 19, 1922.

UNITED STATES PATENT OFFICE.

LINWOOD T. RICHARDSON, 01? NEW BBUNSVJICK, NEW JERSEY, ASSIGNOR TO THE CUTLER-HAMMER (30., OF I 'IILXVAUKEE, WISCONSIN, CORPORATION OF WISCONSIN.

METHOD OF MAKING ELECTRICAL RESISTANCE UNITS AND THE LIKE.

No Drawing.

Be it known that I. lnNnoor: T. la,l(,".[.\lli)- soN, a cit zen o the United States. residing at New Brunswick. in the county 0? Middlesex and State o'l New J cy, have invented new and us fill lmpro'ren'lents in Methods of Making Electrical. Resistance llnits and the like, of which the tollo inn; is a itull clear, concise, and exact description. reterence being had to the accompanying: drawing; forming a part of this specification.

This invention relates to a method of malt ing electrical resistance units and the like having vitreous or other fired coatings.

The type of resistance unit to which the present invention is particularly applicable is that wherein an insulating base. which may comprise .)orcelain or other more or less readily fusible material either with without a metallic nucleus. and ol circular or other cross section. is exteriorly wound with nun'lerous turns of resistor such as wire. such turns being insulated from one another through. suitable spacing or otherwise and being ordinarily connected with suitable terminals fixed to the base.

It is customary. and in most cases absolutely essential, that such turns of the resistor be exteriorly protected and .iirmly retained in suitable position by means oi an insulating coating adhering thereto and to the base and where such COfltin is ot a character rcrpiirin;- fusion at relatively cle Vated temperatures great dilliculty has heretotore been encountered in successfully applying such coating to this type of articles.

\Vhen substantially homogeneous bases of porcelain or the like are employed the cause of much dilliculty has l'lCOll. Found to reside in the, fact that the resistors ordinarily eu|- ployed for such purposes have a much higher coejllicient ol' expansion than that; ol' the material of the base wherein." dnringr heat treatment the various turns of the re s stor expand to a greater or I or extent and become loose upon the base allluuurjh tightly wound thereon at ordinary tenipcu atures.

Thus ii the coating he applied in plastic condition to the wound unit. the same though adhering at ordinary temperatures nevertheless under the high tem 'ieratures required for fusion is apt to become loosened and more or less separated from the base a lication filed October 27, 1920. Serial No. 420,056.

due to the a'l crenientioned expansion oi the encircling res tor. h loreoyer, the turns oli the resistor heinn' thus released from their retention in intimate contact with thr haso tend to adjust themselves For their own increased length hy lateral shil'thigwherrln. the turns oi the resistor are otten eft 1 posed or in such close proximity as to cause Short-circuiting.

The present invention has among; its ohjccts that of overcoming the 'l'oren'oinsr (iii-- liculties and disadvanta -es in the production of articles oil the a,toreinentioned character.

Other objects and advantages will hereinafter appear.

According to the present invention it is proposed to confine the unit during the heat treatment necessary for fusion oi the coating? thereoi and to ffect such coi'ilinenient by emhcddine' the unit in a medium which substantially inert as regards the constituents oi the coating: undergoino; treatn'ient at least at the temperatures involved. such medium being: moreover of snflicient density to resist the aforementioned tendency of the resistor to shift under the influence of the applied heat. It been found in practice that ordinary sand of about 40 mesh constitutes an excellent material in which to embed such units during heat treatment thereof.

A. preferred manner of 1a rrying out the i'n-esent method may be stated as Follows. The resistor being wound or otherwise applied to the insulating; base in accordance with known methods. a low melting point class is prepared in any one of a. plurality o'l known ways and is thereafter finely ,tfround. mixed wilh water or other medium lor the formation iii apaste and. applied to the wound unit by di 'ipin r. pouring: or oil'lcrwise.

The unit as thus coated thereafter dried to expe the Water or other snltistani're used in Forming the paste.

l'ter drying' the unit is lirmly embedded in a ql'lantity o'li' ordinary sand preferably about 40 mesh and placed in a kiln such jlior instance. as that employed in glazing potte ry, whereby the temperature of the unit is raised to a point suflicient for effecting fusion of the glass with which it is coated. As soon as such coating is thoroughly fused the unit still. embedded in the sand is re-- mored dlHl permitted to cool. Theunitmay he TQHlOVGtl "from the sand. at any time fol.- lowing cooling thereof to a temperature sullicie' tly low to permit setting of the coat- 111g.

Such embedding of the unit prior to heat treatment provides against disintegration or tained. Further, the presence of the surrounding sand serves to retard both the heating and the cooling" of the unit thereby obviating the danger of cracking of the base due to sudden temperature changes.

In practice the sand is preferably contained in a relatively large tray of cast iron or other suitable material and of a size suiiicient to accommodate a relatively large number oi ordinary units, the latter being packed in the sand relatively close to one another. However, a suitable intervening layer of sand is maintained at all points to insure the necessary spacing between adjacent units. The tray so charged may then be introduced into and removed from the kiln without regard to numerous of the precautions heretofore required in handling the single units.

By the foregoing method the output ot the kiln or furnace is greatly increasedv over that possible by prior methods, the quality of the product being very markedly im proved and the number of pieces damaged during heat treatment being minimized.

hat I claim as new and desire to secure by Letters Patent is:

1. The method of heat treating resistance units and the like, which comprises embedding such units, prior to treatment, in a dense body or medium which, is chemically inactive under the conditions imposed by the treatment, and effecting heat treatment of such units while so embedded.

2. The method of heat treating resistance units and the like which comprises embed ding such units in sand and effecting heat treatment of the units while so embedded.

3. The method of firing an electrical resistance unit having a resistor encircling a base, the resistor to be bonded to the base by a fusible coating, which comprises embedding such unitin a dense body or medium which is chemically inactive with respect to such coating and then heat treating the unit while so embedded.

4. The method of firing an electrical resistanee unit having an insulating base, a surrounding resistor of higher heat expansion coefficient than said base and a coating to be fired, which comprises embedding such unit in a body of sand and efleeting heat treatment oi the unit while so embedded.

In witness whereof, I have hereunto subscribed my name.

LINWOOD r. Rronannson 

